Prior and current diagnostic blood collection tubes having a highly toxic reagent disposed therein prior to taking a blood sample have had several major problems. One of the most serious is that of reagent reflux back through the needle contaminating the patient. Antibackflow devices have been utilized to remedy the problem of reagent reflux but have been proven inadequate.
Another disadvantage is that the blood sample interacts with the reagent immediately upon being drawn into the sample collection tube. Thus the reaction time of the reagent and blood sample cannot be measured or controlled. Anticoagulants or other sample preservatives cannot be added to the tube with the reagent since they are incompatible. Therefore, it is not possible to preserve the sample in the tube.